1. Field of the Invention
The present invention relates to an electrophotographic photosensitive member, a process cartridge having an electrophotographic photosensitive member and an electrophotographic apparatus.
2. Description of the Related Art
Recently, as a photoconductive substance (a charge generating material and a charge transporting material) used in an electrophotographic photosensitive member, which is installed in an electrophotographic apparatus, development of organic photoconductive substances have been aggressively performed.
The electrophotographic photosensitive member (organic electrophotographic photosensitive member) using an organic photoconductive substance usually has a photosensitive layer, which is formed by applying a coating solution obtained by dissolving and/or dispersing an organic photoconductive substance and a binder resin in a solvent, onto a support, and drying it. Furthermore, as the layer structure of a photosensitive layer, a laminate type (successive layer type) is generally employed, which is formed by stacking a charge generation layer and a charge transport layer successively in this order on a support.
An electrophotographic photosensitive member using an organic photoconductive substance does not always satisfy all characteristics required for an electrophotographic photosensitive member at high levels. In the electrophotographic process, various types of members such as a developer, a charging member, a cleaning blade, a paper sheet and a transfer member (hereinafter referred also to as “contact members”) come into contact with the surface of the electrophotographic photosensitive member. As a characteristic required for an electrophotographic photosensitive member, reducing image deterioration caused by contact stress with these contact members may be mentioned. Particularly, as the durability of an electrophotographic photosensitive member improves in recent years, it has been desired to maintain the effect of reducing image deterioration caused by the contact stress.
As to mitigating the contact stress, it has been proposed to add a siloxane modified resin, which has a siloxane structure in a molecular chain, to the surface layer of an electrophotographic photosensitive member to be in contact with the contact members. For example, Japanese Patent Application Laid-Open No. H11-143106 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2007-199688 (Patent Document 2) disclose a resin having a siloxane structure integrated into a polycarbonate resin. Japanese Patent Application Laid-Open No. H03-185451 (Patent Document 3) discloses a resin having a siloxane structure integrated into a polyester resin. Japanese Patent Application Laid-Open No. H11-194522 (Patent Document 4) discloses a resin having a cyclic siloxane structure integrated into a polyester resin. Japanese Patent Application Laid-Open No. 2000-075533 (Patent Document 5) discloses a resin having a branched siloxane structure integrated therein. Japanese Patent Application Laid-Open No. 2002-128883 (Patent Document 6) discloses a resin having a siloxane structure integrated at an end of a polyester resin. Japanese Patent Application Laid-Open No. 2003-302780 (Patent Document 7) discloses a technique for adding a polyester resin having a siloxane structure and a compound having a polymerizable functional group to the surface layer of an electrophotographic photosensitive member.
However, the polycarbonate resins disclosed in Patent Documents 1 and 2, are inferior in mechanical strength compared to the polyester resin, in particular, an aromatic polyester resin. Therefore, they may not be sufficient in order to satisfy durability improvement recently required in balance. Furthermore, in the resins disclosed in Patent Documents 1 and 2, there is a polycarbonate resin having a siloxane structure integrated therein migrating to the surface of a surface layer when a plurality of types of resins is used in combination in the surface layer. This is an effective approach in mitigating the contact stress in the beginning of use of an electrophotographic photosensitive member; however, this approach may not be sufficient in view of persistency of the effect.
Furthermore, a compound having a benzidine skeleton serving as a charge transporting material contained in the charge transport layer, is one of the materials having high electrophotographic characteristics. However, some of the resins disclosed in Patent Documents 1 and 2 cause aggregation of the compound having a benzidine skeleton in the resin, thereby decreasing potential stability during repeated use.
Furthermore, the polyester resin disclosed in Patent Document 3 is a resin obtained by block copolymerization of a siloxane structure and an aromatic polyester structure. However, a charge transporting material tends to aggregate in this resin, decreasing potential stability during repeated use.
Furthermore, the resin disclosed in Patent Document 4 is excellent in mechanical strength; however, the effect of mitigating the contact stress may not be sufficient.
Furthermore, the resin disclosed in Patent Document 5 is excellent in mitigating the contact stress; however, a charge transporting material tends to be aggregated in the resin and potential stability during repeated use may decrease in some cases.
Furthermore, in the resin disclosed in Patent Document 6, the effect of mitigating the contact stress is not sufficient. Furthermore, when a plurality of resins is used in combination in the surface layer, the resin disclosed in Patent Document 6 tends to migrate to the surface of the surface layer. Therefore, it is not sufficient in view of persistency of the effect.
Furthermore, the resin disclosed in Patent Document 7 is not sufficient in view of mitigation of the contact stress and, in addition, a charge transporting material tends to aggregate in the resin and potential stability decreases during repeated use in some cases.